Stepped frequency radar systems with spectral agility

ABSTRACT

A stepped frequency radar system is disclosed. The system includes components for performing stepped frequency scanning across a frequency range using frequency steps of a step size, the stepped frequency scanning performed using at least one transmit antenna and a two-dimensional array of receive antennas, changing at least one of the step size and the frequency range, and performing stepped frequency scanning using the at least one transmit antenna and the two-dimensional array of receive antennas and using the changed at least one of the step size and the frequency range.

BACKGROUND

Radar detection involves transmitting electromagnetic energy andreceiving reflected portions of the transmitted electromagnetic energy.Techniques for transmitting electromagnetic energy in radar systemsinclude impulse, chirp, and stepped frequency techniques. Steppedfrequency radar has traditionally been implemented by repeatedlyscanning over the same frequency range using the same step size. Forexample, a frequency burst of stepped frequency pulses over the samefrequency range with the same step size and the same number of steps iscontinuously repeated to implement stepped frequency radar. Althoughtraditional stepped frequency radar works well, there is a need toexpand the capabilities of stepped frequency radar.

SUMMARY

A stepped frequency radar system is disclosed. The system includescomponents for performing stepped frequency scanning across a frequencyrange using frequency steps of a step size, the stepped frequencyscanning performed using at least one transmit antenna and atwo-dimensional array of receive antennas, changing at least one of thestep size and the frequency range, and performing stepped frequencyscanning using the at least one transmit antenna and the two-dimensionalarray of receive antennas and using the changed at least one of the stepsize and the frequency range.

Other aspects in accordance with the invention will become apparent fromthe following detailed description, taken in conjunction with theaccompanying drawings, illustrated by way of example of the principlesof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C depict frequency versus time graphs of impulse, chirp, andstepped frequency techniques for transmitting electromagnetic energy ina radar system.

FIG. 2 depicts a burst of electromagnetic energy using stepped frequencytransmission.

FIG. 3A depicts a graph of the transmission bandwidth, B, of transmittedelectromagnetic energy in the frequency range of 2-6 GHz.

FIG. 3B depicts a graph of stepped frequency pulses that have arepetition interval, T, and a step size, Δf, of 62.5 MHz.

FIG. 4A depicts a frequency versus time graph of transmission pulses,with transmit (TX) interval and receive (RX) intervals identifiedrelative to the pulses.

FIG. 4B depicts an amplitude versus time graph of the transmissionwaveforms that corresponds to FIG. 16A.

FIG. 5 illustrates operations related to transmitting, receiving, andprocessing phases of the sensor system operation.

FIG. 6 depicts a functional block diagram of an embodiment of a sensorsystem that utilizes millimeter range radio waves.

FIG. 7 depicts an expanded view of an embodiment of portions of thesensor system of FIG. 6, including elements of the RF front-end.

FIG. 8 depicts an embodiment of the IF/BB component shown in FIG. 7.

FIG. 9 illustrates the frequency range of 2-6 GHz relative to differentrange scales.

FIG. 10 depicts the frequency range of 2-6 GHz relative to a range scaleof 256.

FIG. 11 is a process flow diagram of operation of stepped frequencyradar scanning.

FIG. 12 depicts a feedback loop between the transmit and receiveelements of the sensor system described with reference to FIGS. 6 and 7.

FIGS. 13A and 13B illustrate two different examples of a scanningoperation, which involves scanning a relatively wide frequency range ata first step size and scanning a more narrow frequency range at asmaller step size or step sizes.

FIGS. 14A and 14B illustrate digital frequency control signals thatcorrespond to the stepped frequency scanning operations illustrated inFIGS. 13A and 13B, respectively.

FIG. 15A illustrates an example of frequency hopping in a steppedfrequency scanning operation.

FIG. 15B illustrates digital frequency control signals that correspondto the frequency hopping operation illustrated in FIG. 15A.

FIG. 16 illustrates an example of a case in which frequency hopping isimplemented in stepped frequency radar to avoid frequency bands of knowninterference.

FIG. 17 illustrates a process in which a frequency range is firstscanned to identify an interfering frequency band and then thesubsequent scan is controlled to hop over the identified interferingfrequency band.

FIG. 18A illustrates stepped frequency scanning over the 2-6 GHzfrequency range in which ranging scanning is performed over the entire2-6 GHz frequency range simultaneously with imaging scanning that isperformed over only the 4-5 GHz frequency range.

FIG. 18B illustrates digital frequency coding for the stepped frequencyscanning illustrated in FIG. 18A.

FIG. 18C illustrates another example of digital frequency coding for thestepped frequency scanning illustrated in FIG. 18A.

FIG. 19A depicts an area that includes two sensor systems, such as thesensor systems described with reference to FIGS. 6-8, which mayinterfere with each other.

FIG. 19B illustrates encoding and corresponding decoding of discretefrequency pulses transmitted from the two sensor systems depicted inFIG. 19A.

FIG. 20 depicts an expanded view of an embodiment of portions of thesensor system of FIG. 6, including elements of the RF front-end.

FIG. 21A depicts and embodiment of a 2×2 array of sensor systems such asthe sensors systems described with reference to FIGS. 6-8.

FIG. 21B illustrates an example of transmission frequency diversity thatcan be implemented by the sensor array of FIG. 23A.

FIG. 22 is an embodiment of a DSP that includes a ranging component andan imaging component.

Throughout the description, similar reference numbers may be used toidentify similar elements.

DETAILED DESCRIPTION

It will be readily understood that the components of the embodiments asgenerally described herein and illustrated in the appended figures couldbe arranged and designed in a wide variety of different configurations.Thus, the following more detailed description of various embodiments, asrepresented in the figures, is not intended to limit the scope of thepresent disclosure, but is merely representative of various embodiments.While the various aspects of the embodiments are presented in drawings,the drawings are not necessarily drawn to scale unless specificallyindicated.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by this detailed description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

Reference throughout this specification to features, advantages, orsimilar language does not imply that all of the features and advantagesthat may be realized with the present invention should be or are in anysingle embodiment of the invention. Rather, language referring to thefeatures and advantages is understood to mean that a specific feature,advantage, or characteristic described in connection with an embodimentis included in at least one embodiment of the present invention. Thus,discussions of the features and advantages, and similar language,throughout this specification may, but do not necessarily, refer to thesame embodiment.

Furthermore, the described features, advantages, and characteristics ofthe invention may be combined in any suitable manner in one or moreembodiments. One skilled in the relevant art will recognize, in light ofthe description herein, that the invention can be practiced without oneor more of the specific features or advantages of a particularembodiment. In other instances, additional features and advantages maybe recognized in certain embodiments that may not be present in allembodiments of the invention.

Reference throughout this specification to “one embodiment”, “anembodiment”, or similar language means that a particular feature,structure, or characteristic described in connection with the indicatedembodiment is included in at least one embodiment of the presentinvention. Thus, the phrases “in one embodiment”, “in an embodiment”,and similar language throughout this specification may, but do notnecessarily, all refer to the same embodiment.

As is known in the field, radar detection involves transmittingelectromagnetic energy and receiving reflected portions of thetransmitted electromagnetic energy. Techniques for transmittingelectromagnetic energy in radar systems include impulse, chirp, andstepped frequency techniques.

FIGS. 1A-1C depict frequency versus time graphs of impulse, chirp, andstepped frequency techniques for transmitting electromagnetic energy ina radar system. FIG. 1A depicts a radar transmission technique thatinvolves transmitting pulses of electromagnetic energy at the samefrequency for each pulse, referred to as “impulse” transmission. In theexample of FIG. 1A, each pulse is at frequency, f₁, and lasts for aconstant interval of approximately 2 ns. The pulses are each separatedby approximately 2 ns.

FIG. 1B depicts a radar transmission technique that involvestransmitting pulses of electromagnetic energy at an increasing frequencyfor each interval, referred to herein as “chirp” transmission. In theexample of FIG. 1B, each chirp increases in frequency from frequency f₀to f₁ over an interval of 2 ns and each chirp is separated by 2 ns. Inother embodiments, the chirps may be separated by very short intervals(e.g., a fraction of a nanosecond) or no interval.

FIG. 1C depicts a radar transmission technique that involvestransmitting pulses of electromagnetic energy at the same frequencyduring a particular pulse but at an increased frequency frompulse-to-pulse, referred to herein as a “stepped frequency” transmissionor a stepped frequency pattern. In the example of FIG. 1C, each pulsehas a constant frequency over the interval of the pulse (e.g., over 2ns), but the frequency increases by an increment of Δf (referred to as a“step size”) from pulse-to-pulse. For example, the frequency of thefirst pulse is f₀, the frequency of the second pulse is f₀+Δf, thefrequency of the third pulse is f₀+2Δf, and the frequency of the fourthpulse is f₀+3Δf, and so on.

In an embodiment, the sensor system described herein is operated usingstepped frequency transmissions to implement stepped frequency scanning.Operation of the sensor system using stepped frequency transmissions toimplement stepped frequency scanning is described in more detail below.FIG. 2 depicts a burst of electromagnetic energy over a frequency rangethat includes multiple steps using stepped frequency transmission. Thefrequency of the pulses in the multi-step burst can be expressed as:

f _(n) =f ₀ +nΔf

where f₀=starting carrier frequency, Δf=step size, τ=pulse length(active, per frequency), T=repetition interval, n=1, . . . N, each burstconsists of N pulses (frequencies) and a coherent processing interval(CPI)=N⋅T=1 full burst. In an embodiment, the repetition intervalcorresponds to the sweep rate of the stepped frequency scanning and thewidth of the full burst is referred to as the frequency range or thestepped frequency scanning range.

Using stepped frequency scanning enables relatively high rangeresolution. High range resolution can be advantageous in ranging and 3Dradar imaging, which can have applications such as identifying objects,e.g., a weapon on a person that may, for example, be made of areflective material and that may have a size in the range of 25 cm×12cm, e.g., the size of a typical handgun. In an embodiment, in order toeffectively isolate a signal that corresponds to reflections ofelectromagnetic energy from an object such as a hand-held weapon, it isdesirable to have a corresponding range resolution, which may beprovided by the 2-6 GHz frequency range.

Using stepped frequency scanning, range resolution can be expressed as:

ΔR=c/2B

wherein c=speed of light, B=effective bandwidth. The range resolutioncan then be expressed as:

ΔR=c/2N⋅Δf

wherein B=N⋅Δf. Thus, range resolution does not depend on instantaneousbandwidth and the range resolution can be increased arbitrarily byincreasing N⋅Δf.

In an embodiment, electromagnetic energy is transmitted from at leastone antenna (referred to as a “TX antenna”) of a stepped frequency radarsystem in the frequency range of approximately 2-6 GHz, whichcorresponds to a total bandwidth of approximately 4 GHz, e.g., B=4 GHz.FIG. 3A depicts a graph of the transmission bandwidth, B, of transmittedelectromagnetic energy in the frequency range of 2-6 GHz. Within a 4 GHzbandwidth, from 2-6 GHz, discrete frequencies (e.g., frequency pulseseach centered at a different frequency) can be transmitted. For example,in an embodiment, the number of discrete frequencies that can betransmitted ranges from, for example, 64-1,024 discrete frequencies,e.g., 64, 128, 256, 512, or 1,024 discrete frequencies. In a case inwhich 64 discrete frequencies are available and a repetition interval,T, over 4 GHz of bandwidth, the step size, Δf, is 62.5 MHz (e.g., 4 GHzof bandwidth divided by 64=62.5 MHz) and in a case with 256 discretefrequencies available and a repetition interval, T, over 4 GHz ofbandwidth, the step size, Δf, is 15.625 MHz (e.g., 4 GHz of bandwidthdivided by 256=15.625 MHz).

FIG. 3B depicts a graph of stepped frequency pulses that have arepetition interval, T, and a step size, Δf, of 62.5 MHz (e.g., 4 GHz ofbandwidth divided by 64=62.5 MHz). As is described below, an examplesensor system may have two TX antennas and four receive (RX) antennas.Assuming a discrete frequency can be received on each RX antenna,degrees of freedom (DOF) of the sensor system in the receive operationscan be expressed as: 4 RX antennas×64 discrete frequencies=256 DOF; and4 RX antennas×256 discrete frequencies=1K DOF. The number of degrees offreedom (also referred to as “transmission frequency diversity”) canprovide signal diversity, which can be beneficial in 3D radar imaging.For example, the different discrete frequencies may have differentresponses to different objects, e.g., different types of weapons. Thus,greater transmission frequency diversity can translate to greater signaldiversity, and ultimately to more accurate 3D radar imaging.

One feature of stepped frequency radar is that the sensor systemreceives reflected electromagnetic energy at basically the samefrequency over the repetition interval, T. That is, as opposed to chirptransmission, the frequency of the pulse does not change over theinterval of the pulse and therefore the received reflectedelectromagnetic energy is at the same frequency as the transmittedelectromagnetic energy for the respective interval. FIG. 4A depictsstepped frequency scanning as a frequency versus time graph oftransmission pulses, with transmit (TX) and receive (RX) intervalsidentified relative to the pulses. As illustrated in FIG. 4A, RXoperations for the first pulse occur during the pulse length, τ, ofrepetition interval, T, and during the interval between the next pulse.FIG. 4B depicts an amplitude versus time graph of the transmissionwaveforms that corresponds to FIG. 4A. As illustrated in FIG. 4B, theamplitude of the pulses is constant while the frequency increases by Δfat each repetition interval, T.

In an embodiment, the power of the transmitted electromagnetic energycan be set to achieve a desired transmission distance and/or a desired.In an embodiment, the transmission power from the TX antennas is about20 dBm.

In an embodiment, electromagnetic energy can be transmitted from the TXantennas one TX antenna at a time (referred to herein as “transmitdiversity”). For example, a signal is transmitted from a first one oftwo TX antennas while the second one of the two TX antennas is idle andthen a signal is transmitted from the second TX antenna while the firstTX antenna is idle. Transmit diversity may reveal that illumination fromone of the two TX antennas provides a higher quality signal thanillumination from the other of two TX antennas. This may be especiallytrue when trying to identify an object such as a person or a weaponcarried by a person. Thus, transmit diversity can provide sets ofreceived signals that are independent of each other and may havedifferent characteristics, e.g., signal power, SNR, etc.

Some theory related to operating a stepped frequency radar system toimplement stepped frequency scanning is described with reference to FIG.5, which illustrates operations related to transmitting, receiving, andprocessing phases of a sensor system operation. With reference to theupper portion of FIG. 5, a time versus amplitude graph of a transmittedsignal burst, similar to the graph of FIG. 4B, is shown. The graphrepresents the waveforms of five pulses of a burst at frequencies of f₀,f₀+Δf, f₀+2Δf, f₀+3Δf, and f₀+4Δf.

The middle portion of FIG. 5 represents values of received signals thatcorrespond to the amplitude, phase, and frequency of each pulse in theburst of four pulses. In an embodiment, received signals are placed inrange bins such that there is one complex sample per range bin perfrequency. Inverse Discrete Fourier Transforms (IDFTs) are thenperformed on a per-range bin basis to determine range information. Thebottom portion of FIG. 5 illustrates an IDFT process that produces asignal that corresponds to the range of a particular object. Forexample, the range may correspond to an object such as a person or aweapon carried by a person. In stepped frequency radar, the process oftransmitting the frequency pulses in bursts of N pulses is repeated overthe same frequency range to determine the range of object. Additionally,the process can be repeated using a 2D array of receive antennas toobtain 2D information that can be used for 2D and/or 3D imaging. In anembodiment, some portion of the signal processing is performed digitallyby a DSP or CPU. Although one example of a signal processing scheme isdescribed with reference to FIG. 5, other signal processing schemes maybe implemented to isolate signals that correspond to reflections fromobjects of interest from signals that correspond to reflections fromother undesired objects and from signals that correspond to leakage fromthe TX antennas.

As described above with reference to FIGS. 1C-5, stepped frequency radarscanning is typically implemented by repeatedly scanning over the samefrequency range (e.g., one full burst) with multiple RF pulses thatincrease in frequency by the same step size. For example, with referenceto FIGS. 3B, 4A, and 4B, a frequency burst of stepped frequency pulsesover the same frequency range with the same step size and the samenumber of steps is repeatedly transmitted to implement stepped frequencyscanning. However, it has been realized that digital control of discretefrequencies in a stepped frequency radar system enables approaches tostepped frequency RF scanning and applications for stepped frequencyradar that heretofore have not been envisioned. For example, digitalcontrol of discrete frequencies in a stepped frequency radar systemenables the step size, frequency range, and/or discrete frequencies tobe changed during a stepped frequency scanning operation in variousunique ways. In an embodiment, the step size can be changed to a smallerstep size to, for example, provide greater imaging resolution within aparticular frequency band of interest. In some instances, the step sizecan be changed “on-the-fly” in response to feedback from the steppedfrequency scanning and in other instances a change in step size can bepreprogrammed. In another embodiment, the scanned frequency range can bechanged to avoid, or “hop” over, a frequency band that may interferewith the scanning operation. Frequency hopping may be implemented to,for example, avoid frequency bands that are known to cause interferenceand/or frequency hopping may be adapted to avoid interfering frequencybands that are learned by the system. In another embodiment,simultaneous stepped frequency scanning for ranging and steppedfrequency scanning for imaging (e.g., 2D or 3D imaging) can beaccomplished by selectively associating digital scanning data withdifferent ranging and imaging data buckets for digital processing. Inanother embodiment, interference between two stepped frequency radarsystems can be mitigated by encoding the discrete frequencies of thestepped frequency scanning (e.g., in a pseudorandom manner) so thatfrequency pulses at the same frequency are unlikely to be transmitted bytwo stepped frequency radar systems at the same time. As is describedbelow, digital control of discrete frequencies in a stepped frequencyradar system provides spectral agility that can be utilized to implementapproaches to stepped frequency scanning and applications for steppedfrequency radar that heretofore have not been envisioned.

FIG. 6 depicts a functional block diagram of an embodiment of a sensorsystem 610 that utilizes millimeter range radio waves to implementstepped frequency radar to implement operations such as ranging andimaging, including 2D or 3D imaging. The sensor system includes transmit(TX) antennas 644, receive (RX) antennas 646, an RF front-end 648, adigital baseband system 650, and a CPU 652. The components of the sensorsystem may be integrated together in various ways. For example, somecombination of components may be fabricated on the same semiconductorsubstrate and/or included in the same packaged IC device or acombination of packaged IC devices. In an embodiment, the sensor systemis designed to transmit and receive radio waves in the range of 2-6 GHzand/or in the range of 122-126 GHz. The sensor system may also operatein other frequency ranges, such as in a range around 24 GHz and/or in arange around 60 GHz,

In the embodiment of FIG. 6, the sensor system 610 includes two TXantennas 544 and four RX antennas 646. Although two TX and four RXantennas are used, there could be another number of antennas, e.g., oneor more TX antennas and three or more RX antennas. In an embodiment, theRX antennas are configured in a 2D array. In an embodiment, the TX andRX antennas are configured to transmit and receive radio waves,respectively. For example, the antennas are configured to transmit andreceive radio waves in the 2-6 GHz frequency range, e.g., wavelengths inthe range of 149.89-149.96 mm and/or in the 122-126 GHz frequency range,e.g., wavelengths in the range of 2.46-2.38 mm.

In the embodiment of FIG. 6, the RF front-end 648 includes a transmit(TX) component 654, a receive (RX) component 656, a frequencysynthesizer 658, and an analogue processing component 660. The transmitcomponent may include elements such as power amplifiers (PAs) andmixers. The receive component may include elements such as low noiseamplifiers (LNAs), variable gain amplifiers (VGAs), and mixers. Thefrequency synthesizer includes elements to generate electrical signalsat frequencies that are used by the transmit and receive components. Inan embodiment, the frequency synthesizer may include elements such as acrystal oscillator, a phase-locked loop (PLL), a frequency doubler,and/or a combination thereof. In an embodiment, the frequencysynthesizer is digitally controlled by digital frequency control signalsreceived from the digital baseband system. The analogue processingcomponent may include elements such as mixers and filters, e.g., lowpass filters (LPFs). In an embodiment, components of the RF front-endare implemented in hardware as electronic circuits that are fabricatedon the same semiconductor substrate.

The digital baseband system 650 includes an analog-to-digital converter(ADC) 662, a digital signal processor (DSP) 664, and a microcontrollerunit (MCU) 666. Although the digital baseband system is shown asincluding certain elements, the digital baseband system may include someother configuration, including some other combination of elements. Thedigital baseband system is connected to the CPU 652 via a bus.

FIG. 7 depicts an expanded view of an embodiment of portions of thesensor system 610 of FIG. 6, including elements of the RF front-end 648that are configured to operate in the 2-6 GHz frequency range. In theembodiment of FIG. 7, the elements include a crystal oscillator 770, aphase locked loop (PLL) 772 (e.g., a digitally controlled PLL), abandpass filter (BPF) 774, power amplifiers (PAs) 778, TX antennas 744,a frequency divider 784, a mixer 786, an RX antenna 746, a low noiseamplifier (LNA) 788, a mixer 792, and an Intermediate Frequency/Baseband(IF/BB) component 794. As illustrated in FIG. 7, the group of receivecomponents identified within dashed box 796 is repeated four times,e.g., once for each of four distinct RX antennas.

Operation of the system shown in FIG. 7 is described with reference to atransmit operation and with reference to a receive operation. In anembodiment, stepped frequency scanning refers collectively to thetransmit and receive operations. The description of a transmit operationgenerally corresponds to a left-to-right progression in FIG. 7 anddescription of a receive operation generally corresponds to aright-to-left progression in FIG. 7. With regard to the transmitoperation, the crystal oscillator 770 generates an analog signal at afrequency of 10 MHz. The 10 MHz signal is provided to the PLL 772 and tothe frequency divider 784. The PLL uses the 10 MHz signal to generate ananalog signal that is in the 2-6 GHz frequency range. In an embodiment,the PLL is digitally controlled in response to digital frequency controlsignals (e.g., N bit control signals, where N is an integer of 1 ormore) that set the desired output frequency of the PLL. The 2-6 GHzsignal is provided to the BPF 774, which filters the input signal andpasses a signal in the 2-6 GHz range to the PAs 778. The 2-6 GHz signalis also provided to the mixer 786.

The power amplifiers 778 amplify the RF signals in the 2-6 GHz rangethat are output from the TX antennas 744. In some embodiments, RF energyis transmitted from both antennas simultaneously and in otherembodiments, RF energy is transmitted from only one TX antenna at atime, or from different subsets of TX antennas depending on how many TXantennas there are in the system. In an embodiment, the 2-6 GHz signalsare output at 20 dBm (decibels (dB) with reference to 1 milliwatt (mW)).In an embodiment and as described below, the PLL 772 is digitallycontrolled to generate discrete frequency pulses between 2-6 GHz thatare used for stepped frequency scanning. For example, as is described inmore detail below, the 2-6 GHz frequency range can be divided intomultiple distinct frequencies, e.g., up to 1,024 discrete frequenciesthat can be individually identified and selected through digitalfrequency control signals.

Dropping down in FIG. 7, the 10 MHz signal from the crystal oscillator770 is also provided to the frequency divider 784, which divides thefrequency down, e.g., from 10 MHz to 2.5 MHz via, for example, twodivide by two operations, and provides an output signal at 2.5 MHz tothe mixer 786. The mixer 786 also receives the 2-6 GHz signal from theBPF 774 and provides a signal at 2-6 GHz+2.5 MHz to the mixer 792 forreceive signal processing.

With reference to a receive operation, electromagnetic (EM) energy isreceived at the RX antenna 746 and converted to electrical signals,e.g., voltage and current. For example, electromagnetic energy in the2-6 GHz frequency band is converted to an electrical signal thatcorresponds in frequency (e.g., GHz), magnitude (e.g., power in dBm),and phase to the electromagnetic energy that is received at the RXantenna. The electrical signal is provided to the LNA 788. In anembodiment, the LNA amplifies signals in the 2-6 GHz frequency range andoutputs an amplified 2-6 GHz signal. The amplified 2-6 GHz signal isthen mixed with the 2-6 GHz+2.5 MHz signal at mixer 792 to generate a2.5 MHz signal that corresponds to the electromagnetic energy that wasreceived at the RX antenna. For example, when a 2 GHz signal is beingtransmitted from the TX antennas and received at the RX antenna, themixer 792 receives a 2 GHz signal that corresponds to theelectromagnetic energy that was received at the antenna and a 2 GHz+2.5MHz signal from the mixer 786. The mixer 792 mixes the 2 GHz signal thatcorresponds to the electromagnetic energy that was received at the RXantenna with the 2 GHz+2.5 MHz signal from the mixer 786 to generate a2.5 MHz signal that corresponds to the electromagnetic energy that wasreceived at the RX antenna. The 2.5 MHz signal that corresponds to theelectromagnetic energy that was received at the RX antenna is providedto the IF/BB component 794 for analog-to-digital conversion. Theabove-described receive process can be implemented in parallel on eachof the four receive paths 796. As is described below, the systemdescribed with reference to FIG. 7 can be used to generate variousdiscrete frequencies that can be used to implement, for example, steppedfrequency radar detection, including stepped frequency radar ranging andstepped frequency radar imaging, e.g., 2D or 3D imaging. As describedabove, multiple mixing operations are performed to implement a sensorsystem as described herein. The multiple mixers and corresponding mixingoperations implement a “compound mixing” architecture that enables useof such frequencies.

FIG. 8 depicts an embodiment of the IF/BB component 794 shown in FIG. 7.The IF/BB component 894 of FIG. 8 includes similar signal paths 802 foreach of the four receive paths/RX antennas and each signal path includesa low pass filter (LPF) 804, an analog-to-digital converter (ADC) 862, amixer 806, and a decimation filter 808. The operation of receive path 1,RX1, is described, although the description applies to each receivepath.

As described above with reference to FIG. 7, the 2.5 MHz signal frommixer 792 (FIG. 7) is provided to the IF/BB component 794/894, inparticular, to the LPF 804 of the IF/BB component 894. In an embodiment,the LPF filters the 2.5 MHz signal to remove negative frequency spectrumand noise outside of the desired bandwidth. After passing through theLPF, the 2.5 MHz signal is provided to the ADC 862, which converts the2.5 MHz signal (e.g., IF signal) to digital data at a sampling rate of10 MHz (e.g., as 12-16 bits of “real” data). The mixer 806 multipliesthe digital data with a complex vector to generate a digital signal(e.g., 12-16 bits of “complex” data), which is also sampled at 10 MHz.Although the signal is sampled at 10 MHz, other sampling rates arepossible, e.g., 20 MHz. The digital data sampled at 10 MHz is providedto the decimation filter 808, which is used to reduce the amount of databy selectively discarding a portion of the sampled data. For example,the decimation filter reduces the amount of data by reducing thesampling rate and getting rid of a certain percentage of the samples,such that fewer samples are retained. The reduction in sample retentioncan be represented by a decimation factor, M, and may be, for example,about 10 or 100 depending on the application, where M equals the inputsample rate divided by the output sample rate.

The output of the decimation filter 806 is digital data that isrepresentative of the electromagnetic energy (e.g., in frequency,amplitude, and/or phase) that was received at the corresponding RXantenna. In an embodiment, samples are output from the IF/BB component894 at rate of 1 MHz (using a decimation factor of 10) or at a rate of100 kHz (using a decimation factor of 100). The digital data is providedto a DSP and/or CPU 864 via a bus 810 for further processing. Forexample, the digital data is processed to perform ranging and/orimaging, which may involve isolating a signal from a particularlocation, e.g., isolating signals that correspond to electromagneticenergy that was reflected from a particular object (e.g., a person or aweapon carried by a person). In an embodiment, stepped frequencyscanning across a frequency range includes the processes of transmittingstepped frequency pulses at discrete frequencies, receiving RF energy,and outputting corresponding digital data. Stepped frequency scanningmay also include processing of the generated digital data to generateranging information, imaging information, and/or some intermediateinformation. In an embodiment, signal processing techniques may beapplied to implement beamforming, Doppler effect processing, and/orleakage mitigation to isolate a desired signal from other undesiredsignals.

In conventional RF systems, the analog-to-digital conversion processinvolves a high direct current (DC), such that the I (“real”) and Q(“complex”) components of the RF signal at DC are lost at the ADC. Usingthe system as described above with reference to FIGS. 6-8, theintermediate frequency, IF, is not baseband, so I and Q can be obtainedafter analog-to-digital conversion and digital mixing as shown in FIG.8.

In an embodiment, certain components of the sensor system are integratedonto a single semiconductor substrate and/or onto a single packaged ICdevice (e.g., a packaged IC device that includes multiple differentsemiconductor substrates (e.g., different die) and antennas). Forexample, elements such as the components of the RF front-end 648, and/orcomponents of the digital baseband system 650 (FIGS. 6-8) are integratedonto the same semiconductor substrate (e.g., the same die). In anembodiment, components of the sensor system are integrated onto a singlesemiconductor substrate that is approximately 5 mm×5 mm.

In an embodiment, digital signal processing of the received signals mayinvolve implementing Kalman filters to smooth out noisy data. In anotherembodiment, digital signal processing of the received signals mayinvolve combining receive chains digitally. Other digital signalprocessing may be used to implement beamforming, Doppler effectprocessing, and ranging. Digital signal processing may be implemented ina DSP and/or in a CPU.

As described above with reference to FIGS. 6 and 7, the frequencysynthesizer (FIG. 6, 658) of the RF front-end (FIG. 6, 648) can generatediscrete frequencies for transmission as frequency pulses (also referredto as discrete frequency pulses) in response to digital frequencycontrol signals received from the digital baseband system (FIG. 6, 650).In an embodiment, the addressable frequency range of the sensor systemis divided into a number of individually addressable discretefrequencies. For example, the addressable frequency range of 2-6 GHz isdivided into 64, 128, 256, 512, or 1,024 individually addressablediscrete frequencies. The number of individually addressable discretefrequencies in turn determines the step size (or vice versa), such that64 discrete frequencies in the 2-6 GHz frequency range corresponds to astep size of 62.5 MHz/step (4 GHz/64=62.5 MHz). Thus, as used herein theterm “range scale” or “RS” refers to the number ofindividually/digitally addressable frequencies that can be generatedusing digital frequency control signals. That is, the range scale (RS)is the scale at which the digitally addressable frequency range isdivided. FIG. 9 illustrates the frequency range of 2-6 GHz relative torange scales of RS64,

RS128, RS256, RS512, and RS1024. In the example illustrated in FIG. 9,for the frequency range of 2-6 GHz, the example range scales andcorresponding step sizes are:

RS64=64 total steps at 62.5 MHz/step;

RS128=128 total steps at 31.25 MHz/step;

RS256=256 total steps at 15.625 MHz/step;

RS512=512 total steps at 7.8125 MHz/step; and

RS1024=1,024 total steps at 3.90625 MHz/step.

Using the approach illustrated in FIG. 9, each discrete frequency isindividually and uniquely identifiable by a number (e.g., which can becommunicated as a digital signal in binary form) depending on the rangescale.

For example, the frequencies of 2 GHz, 3 GHz, 4 GHz, 5 GHz, and 6 GHzcan be individually identified by the respective numeric valuesdepending on the range scale:

1/16/32/48/64 at RS64;

1/32/64/96/128 at RS128;

1/64/128/192/256 at RS256;

1/128/256/384/512 at RS512; and

1/256/512/768/1024 at RS1024.

To further illustrate how numeric values can be used to individuallyidentify discrete frequencies for use in stepped frequency radar, FIG.10 depicts the frequency range of 2-6 GHz relative to a range scale of256 (RS256). As illustrated in FIG. 10, numeric value “1” corresponds to2 GHz, numeric value “64” corresponds to 3 GHz, numeric value “128”corresponds to 4 GHz, numeric value “192” corresponds to 5 GHz, andnumeric value “256” corresponds to 6 GHz. Using the above-describedapproach to identify discrete frequencies, step sizes can be generatedas multiples of the step size of the particular range scale (RS). Forexample, at RS64, it is possible to digitally identify discretefrequency steps at multiples of 62.5 MHz/step, whereas at RS256, it ispossible to digitally identify discrete frequency steps at multiples of15.625 MHz (e.g., 15.625 MHz/step, 31.25 MHz/step, or 62.5 MHz/step), atRS512, it is possible to digitally identify discrete frequency steps atmultiples of 7.8125 MHz (e.g., 7.8125 MHz, 15.625 MHz/step, 31.25MHz/step, or 62.5 MHz/step), and at RS1024, it is possible to digitallyidentify discrete frequency steps at multiples of 3.90625 MHz (e.g.,3.90625 MHz, 7.8125 MHz, 15.625 MHz/step, 31.25 MHz/step, or 62.5MHz/step). In an embodiment, a single range scale (RS) is used todigitally identify a wide range of discrete frequencies and a wide rangeof step sizes. For example, the range scale 1,024 (RS1024) is used todigitally identify a wide range of discrete frequencies and a wide rangeof step sizes. Examples of using digital frequency control signals toimplement stepped frequency scanning in a stepped frequency radar systemare described below.

In accordance with an embodiment of the invention, the step size and/orfrequency range of stepped frequency scanning is changed during ascanning operation. For example, the step size is changed from a firststep size to a second step size and/or the frequency range that isscanned is changed from a first frequency range to a second frequencyrange. FIG. 11 is a process flow diagram of operation of steppedfrequency radar scanning. At block 1102, stepped frequency scanning isperformed across a frequency range using frequency steps of a step size.At decision point 1104, it is determined whether or not the step sizeand/or the frequency range should be changed. Various criteria can beused to determine if and when the step size and/or frequency rangeshould be changed. If at decision point 1104 it is determined that thestep size and/or frequency range should not be changed, then the processreturns to block 1102. If on the other hand, it is determined that thestep size and/or frequency range should be changed, then the processproceeds to block 1106. At block 1106, stepped frequency scanning isperformed with the changed step size and/or frequency range. In anembodiment, the frequency of the transmitted frequency pulses and thestep sizes are controlled by digital frequency control signals andchanges to the step size and/or frequency range are made based onpreprogrammed digital frequency control signals and in otherembodiments, changes to the step size and/or frequency range are made inresponse to feedback information from the received signals.

In an embodiment, at least one parameter of the stepped frequencyscanning is changed in response to feedback information from thereceived signals of the stepped frequency scanning. For example, thestep size and/or scanned frequency range may be changed in response toidentifying an object or in response to an indication that an object maybe present. FIG. 12 depicts a feedback loop between the transmit andreceive elements of the sensor system described above with reference toFIGS. 6-8. In particular, the sensor system depicted in FIG. 12 is thesame as the sensor system depicted in FIG. 7 except that the sensorsystem depicted in FIG. 12 includes the digital baseband system 650 anda feedback loop that is formed by the digital output of the IF/BBcomponent 794 of the RF front-end, the digital baseband system 650, anddigital frequency control signals that are provided to the PLL 772 fromthe digital baseband system 650. Using the feedback loop illustrated inFIG. 12, the discrete frequencies that are generated by the PLL can bedigitally controlled by the digital baseband system in response to anevaluation of digital data received from the IF/BB component 794 of theRF front-end. The particular logic used to evaluate the received digitaldata and to change the step size and/or frequency range can be dependenton many factors, including the particular application in which thesensor system is deployed. Some examples of logic associated withchanging the step size and/or frequency range are described below.Although FIG. 12 illustrates a feedback based control scheme, in otherembodiments, the step size and/or frequency range of the steppedfrequency scanning can be changed according to preprogrammed frequencycontrol signals and/or pre-established rules.

As described above, digital control of discrete frequencies in steppedfrequency radar scanning enables flexible scanning that can be adaptedto implement various features and/or to achieve various goals. Atfrequencies in the 2-6 GHz range, larger step sizes may be moreeffective for ranging (i.e., determining the range of an object) andsmaller step sizes may be more effective for imaging (i.e., determiningthe dimensions of an object, particularly in 2D, e.g., relative to aplane that is perpendicular to a line between the sensor system and theobject). Thus, in one application, it may be desirable to identify therange of an object using frequency pulses transmitted at a first stepsize and to identify a 2D or 3D profile of the object or a relatedobject using frequency pulses transmitted at a second, smaller, stepsize, and possibly at a third, even smaller, step size. For example, ina security sensor application, it may be desirable to use frequencypulses transmitted over a wide frequency range at a first step size toidentify the range of an object (e.g., a person and/or a weapon) andthen use frequency pulses transmitted over a narrower frequency range ata second, smaller, step size to identify the 2D or 3D profile of anobject (e.g., a person and/or a weapon carried by the person). In anembodiment, the particular step sizes and/or frequency ranges areselected/changed/adjusted in real time based on feedback from thereceived signals (e.g., “on-the-fly” adjustment). For example, the stepsizes and/or frequency ranges can be changed on-the-fly in a couple ofrepetition intervals, T. The received signals may change as differentfrequencies reflect off different objects in different ways (e.g., somefrequencies will resonate from a weapon better than other frequencies)and therefore the parameters of the stepped frequency scanning can beadapted on the fly to the current conditions that are being experienced.In an embodiment, smaller step sizes around a specific narrowerfrequency range may be better suited for 2D or 3D imaging of an objectsuch as a weapon due to the relatively high reflectivity of portions ofa weapon (e.g., around a particular frequency range) that tend to besmooth, such as the barrel. Alternatively, parameters (e.g., step sizeand frequency range (frequency range could refer to the differencebetween two frequencies or frequency range could refer to a specificfrequency range that is defined by two absolute frequencies)) of thestepped frequency scanning can be pre-programmed.

FIGS. 13A and 13B illustrate two different examples of a steppedfrequency scanning operation, referred to as a “telescopic,” “zoom,” or“focused” stepped frequency scanning operation, which involves scanninga relatively wide frequency range at a first step size and scanning amore narrow frequency range (or frequency ranges) at a smaller step sizeor step sizes. The example illustrated in FIG. 13A is referred to as an“overlapping” stepped frequency scanning operation and the exampleillustrated in FIG. 13B is referred to as a “non-overlapping” steppedfrequency operation.

With reference to FIG. 13A, a first scan (scan 1) of the frequency rangeof 2-6 GHz is performed at a step size of 62.5 MHz (Δf=62.5 MHz), asecond scan (scan 2) of the frequency range of 4-5 GHz is performed at astep size of 31.25 MHz (Δf=31.25 MHz), and then a third scan (scan 3) ofthe frequency range of approximately 4.2-4.3 GHz is performed at a stepsize of 15.625 MHz (Δf=15.625 MHz). As illustrated in FIG. 13A, scans 1,2, and 3 each separately scan the frequency range of 4.2-4.3 GHz andthus the three scans “overlap” in the 4.2-4.3 GHz frequency range.

With reference to FIG. 13B, a first scan (scan 1) of the frequency rangeof 2-4 GHz is performed at a step size of 62.5 MHz (Δf=62.5 MHz), asecond scan (scan 2) of the frequency range of 4-5 GHz is performed at astep size of 31.25 MHz (Δf=31.25 MHz), a third scan (scan 3) of thefrequency range of approximately 4.2-4.3 GHz is performed at a step sizeof 15.625 MHz (Δf=15.625 MHz), a fourth scan (scan 4) of the frequencyrange of 4.3-5 GHz is performed at a step size of 31.25 MHz (Δf=31.25MHz), and then a fifth scan (scan 5) of the frequency range of 5-6 GHzis performed at a step size of 62.5 MHz (Δf=62.5 MHz). As illustrated inFIG. 13B, scans 1, 2, 3, 4, and 5 all scan over different,non-overlapping, frequency ranges and thus are “non-overlapping” overthe range of 2-6 GHz.

In an embodiment, when using the sensor system for a securityapplication that involves identifying weapons such as handguns, rifles,and knives, including weapons carried by a person, the stepped frequencyscanning may implement some form of the above-described “telescopic,”“zoom,” or “focused” stepped frequency scanning when the reflectedsignals indicate that a more reflective object (e.g., a smooth object)is within range of the sensor system. In one embodiment, an increase inthe magnitude of RF energy at certain wavelengths that correspond toknown sizes of weapons such as handguns, rifles, and knives (e.g., dueto such frequencies resonating off the weapon), may indicate that suchan object is within range of the sensor system. Therefore, in anembodiment, the step size to be used in stepped frequency scanning andthe frequency range to be scanned are adjusted when certain reflectivecharacteristics are detected. In one embodiment, the frequency range isreduced to a frequency range more closely focused on a frequency rangeof interest (e.g., a frequency range that is known through training tocorrespond to resonant wavelengths of a weapon) and the step size isreduced to a step size that can produce 2D profile information that canbe used to determine (e.g., to some degree of certainty) if a weapon maybe present. In an embodiment, in a security sensor application, it maybe desirable to use frequency pulses transmitted at a first step size toidentify the range of an object (e.g., a person and/or a weapon) andupon receiving RF energy that indicates a person is present or that anobject that may be weapon is present, the sensor system changes on thefly to transmitting frequency pulses at a second, smaller, step sizeover a narrower frequency range (e.g., around frequencies that are knownto resonate from a weapon such as a handgun, rifle, or knife) toidentify the 2D or 3D profile of an object (e.g., a person and/or aweapon). In an embodiment, the particular step sizes and/or frequencyranges are selected/changed/adjusted in real time in response toinformation received via the feedback loop of the sensor system asdescribed with reference to FIG. 12.

As described above with reference to FIGS. 9 and 10, the individuallyaddressable discrete frequencies used in the stepped frequency scanningcan be controlled by digital frequency control signals. FIGS. 14A and14B illustrate digital frequency control signals that correspond to thestepped frequency scanning operations illustrated in FIGS. 13A and 13B,respectively. In the examples of FIGS. 14A and 14B, a range scale of256, RS256, is used as the range scale to identify the individuallyaddressable discrete frequencies that are transmitted from the sensorsystem. With reference to FIG. 14A (which corresponds to FIG. 13A), thediscrete frequencies of scans 1, 2, and 3 are identified in a sequential(in time) stream of numeric frequency identifiers. Using an RS256notation, discrete frequencies 4, 8, 12, . . . , 248, 252, and 256 aregenerated and transmitted as frequency pulses to implement scan 1 at astep size of Δf=62.5 MHz. Next, discrete frequencies 128, 130, 132, . .. , 188, 190, and 192 are generated and transmitted as frequency pulsesto implement scan 2 at a step size of Δf=31.25 MHz. Lastly, discretefrequencies 136, 137, 138, 139, 140, 141,and 142 are generated andtransmitted as frequency pulses to implement scan 3 at a step size ofΔf=15.625 MHz.

With reference to FIG. 14B (which corresponds to FIG. 13B), the discretefrequencies of scans 1, 2, 3, 4, and 5 are identified in a sequential(in time) stream of numeric frequency identifiers. Using an RS256notation, discrete frequencies 4, 8, 12, . . . , 124, and 128 aregenerated and transmitted as frequency pulses to implement scan 1 at astep size of Δf=62.5 MHz. Next, discrete frequencies 128, 130, 132, 134,and 136 are generated and transmitted as frequency pulses to implementscan 2 at a step size of Δf=31.25 MHz. Next, discrete frequencies 136,137, 138, 139, 140, 141,and 142 are generated and transmitted asfrequency pulses to implement scan 3 at a step size of Δf=15.625 MHz.Next, discrete frequencies 142, 144, 146, . . . , 188, 190, and 192 aregenerated and transmitted as frequency pulses to implement scan 4 at astep size of Δf=31.25 MHz. Lastly, discrete frequencies 192, 196, 200, .. . , 248, 252, and 256 are generated and transmitted as frequencypulses to implement scan 5 at a step size of Δf=62.5 MHz. As illustratedin FIGS. 13A-14B, digital control of discrete frequencies in a steppedfrequency radar system enables “telescopic,” “zoom,” or “focused”stepped frequency scanning to transmit frequency pulses at a first stepsize to identify the range of an object (e.g., a person and/or a weapon)and then to change the step size and scanned frequency range on the flyto a smaller step size over a narrower frequency range (e.g., aroundfrequencies that are known to resonate from a weapon such as a handgun,rifle, or knife) to identify the 2D or 3D profile of an object (e.g., aperson and/or a weapon).

As described above, digital control of discrete frequencies in steppedfrequency radar scanning enables flexible scanning that can be adaptedto implement various features and/or to achieve various goals. In somecases, it may be desirable to skip or “hop” a particular frequency bandto, for example, avoid a frequency band that may experience interferingRF energy. FIG. 15A illustrates an example of “frequency hopping” in astepped frequency scanning operation relative to the 2-6 GHz frequencyrange and a range scale of 256 (RS256). In the example of FIG. 15A,stepped frequency scanning is performed over a frequency range of 2-6GHz at step size of 62.5 MHz, Δf=62.5 MHz, with the frequency band of4-5 GHz being skipped or “hopped” over. In a stepped frequency scanningoperation, the frequency range of 2-4 GHz is scanned at 62.5 MHz stepsand then the frequency range of 5-6 GHz is scanned at 62.5 MHz steps. Inan embodiment, the stepped frequency scanning is performed at the samesweep rate throughout the scan. That is, the time between frequencysteps is constant (e.g., interval, T, see FIGS. 2, 3B, 4A, and 3B) eventhrough the frequency hop.

As described above with reference to FIGS. 9, 10, 14A, and 14B, thediscrete frequencies used in the stepped frequency scanning can becontrolled by digital frequency control signals. FIG. 15B illustratesdigital frequency control signals that correspond to the steppedfrequency scanning operation illustrated in FIG. 15A. In the example ofFIG. 15B, a range scale of 256, RS256, is used as the range scale toidentify discrete frequencies and the discrete frequencies of the scanare identified in a sequential (in time) stream of numeric frequencyidentifiers. Using an RS256 notation, discrete frequencies 4, 8, 12, . .. , 120, 124, and 128 are generated and corresponding frequency pulsesare transmitted to implement the scan of the 2-4 GHz frequency range ata step size of Δf=62.5 MHz and discrete frequencies 192, 196, 200, . . ., 248, 252, and 256 are generated and corresponding frequency pulses aretransmitted to implement the scan of the 5-6 GHz frequency range at astep size of Δf=62.5 MHz. In the example of FIG. 15B, the digitallycontrolled frequency hop is indicated by a dashed vertical line, whichindicates where the digital frequency control signals jump from numericvalue 128 to 192 in one step. Although the numeric values of the digitalfrequency control signals jump from numeric value 128 to 192, the jumphappens in one step (e.g., one fixed time interval, T) so that there isno added time gap associated with the frequency hop.

The concept of frequency hopping in stepped frequency radar operationsis described above with reference to FIGS. 15A and 15B. In environmentsthat implement a wireless communications protocol such as WIFI, thefrequency bands of 2.412-2.462 GHz and 5.180-5.825 GHz may include RFenergy that could interfere with the sensor system described herein.Therefore, in an embodiment, stepped frequency radar scanning can beperformed in a manner that “hops over” known interfering frequencybands, e.g., the interfering frequency bands of 2.412-2.462 GHz and5.180-5.825 GHz. FIG. 16 illustrates an example of a case in whichfrequency hopping is implemented in stepped frequency radar usingdigital frequency control signals to avoid frequency bands of knowninterference. Specifically, the example of FIG. 16 illustrates frequencyhopping over the WIFI frequency bands of 2.412-2.462 GHz and 5.180-5.825GHz, although the techniques can be applied to other known interferingfrequency bands.

In the example described with reference to FIG. 16, the WIFI frequencybands of 2.412-2.462 GHz and 5.180-5.825 GHz are known. However, inother applications, the existence of interfering RF energy in thesurrounding environment may not be known. Thus, in an embodiment, theexistence of interfering RF energy in the surrounding environment islearned by the sensor system and then the sensor system can adapt thestepped frequency scanning to hop over frequency bands that areidentified to exhibit RF energy that may interfere with steppedfrequency radar operations. FIG. 17 illustrates a process in which afrequency range is first scanned to identify an interfering frequencyband and then the subsequent scan (or scans) hops over the identifiedinterfering frequency band. In an embodiment and as illustrated in FIG.17, first, a learning scan (scan 1) is performed over the entireaddressable frequency range, e.g., 2-6 GHz. In an embodiment, thelearning scan is performed with the transmitter PAs deactivated (e.g.,the PAs 678 in the sensor system depicted in FIG. 6 turned off orotherwise bypassed) and the sensor system scanning the 2-6 GHz frequencyrange for interfering signals. For example, with reference to FIG. 7,the PLL generates discrete frequency pulses in a stepped frequencymanner and the frequency pulses are distributed throughout sensor systemas described with reference to FIG. 7 except that amplified frequencypulses are not transmitted from the TX antennas because the PAs aredeactivated. In the example of FIG. 7, it is assumed that interfering RFenergy is found in the approximately 4.3-4.6 GHz frequency band and sothe stepped frequency scanning is digitally controlled to hop over the4.3-4.6 GHz frequency band. In scan 2, the sensor system is digitallycontrolled to hop over the interfering frequency band using thetechniques described above with reference to FIGS. 15A and 15B.

It has been found that larger frequency steps can be better for rangingand smaller frequency steps can be better for 2D or 3D imaging ofcertain objects of interest such as humans and weapons such as handguns,rifles, and knives. However, performing separate stepped frequency scansfor ranging and imaging takes additional time. Therefore, in anembodiment, stepped frequency scanning is performed to simultaneouslyimplement stepped frequency scanning for two different purposes, e.g.,for “ranging scanning” and for “imaging scanning,” which enables thegeneration of both ranging data and imaging data. FIG. 18A illustratesstepped frequency scanning over the 2-6 GHz frequency range in whichranging scanning is performed over the entire 2-6 GHz frequency rangesimultaneously with imaging scanning that is performed over only the 4-5GHz frequency range. In particular, in the example of FIG. 18A, rangingscanning is performed at a first step size, e.g., Δf=62.5 MHz, andimaging scanning is performed at a second, smaller, step size, e.g.,Δf=15.625 MHz. In order to perform simultaneous ranging scanning andimaging scanning, in an embodiment, over the frequency range of 2-4 GHz,discrete frequencies are stepped at 62.5 MHz/step, then over thefrequency range of 4-5 GHz, discrete frequencies are stepped at 15.625MHz/step, and then over the frequency range of 5-6 GHz, discretefrequencies are stepped again at 62.5 MHz/step. As illustrated in FIG.18A, a single non-overlapping scan across the frequency range of 2-6 GHzincludes frequency bands that are scanned at different step sizes.

FIG. 18B illustrates digital frequency coding (in a time sequence) forthe stepped frequency scanning illustrated in FIG. 18A. At thetransmitter (TX), discrete frequencies are stepped at 62.5 MHz/step,then discrete frequencies are stepped at 15.625 MHz/step, then discretefrequencies are stepped at 62.5 MHz/step. The digital frequency codingusing an RS256 scale includes a first scan segment of frequencies 4, 8,12, . . . , 120, 134, and 128 (Δf=62.5 MHz), a second scan segment offrequencies 129, 130, 131, . . . , 190, 191, and 192 (Δf=15.625 MHz),and a third scan segment of frequencies 196, 200, 204, . . . , 248, 252,and 256 (Δf=62.5 MHz). Reflections corresponding to the transmittedfrequency pulses are received in the same sequential order at thereceiver (RX) of the sensor system 1810 and processed. With reference tothe receive operation, FIG. 18B illustrates that the discrete frequencypulses of the transmitted stream are received in the same sequentialorder (in time) as they are transmitted. The receiver, RX, then placesranging data in a “ranging data bucket” 1820 and places imaging data ina different “imaging data bucket” 1822. In particular, as illustrated inFIG. 18A, the ranging scan involves discrete frequency pulses at a stepsize of 62.5 MHz across the frequency range of 2-6 GHz and the imagingscan involves discrete frequency pulses at a step size of 15.625 MHzacross the frequency range of 4-5 GHz. Thus, with reference to the leftside of the receive operation, the portion of digital data thatcorresponds to the ranging data is placed in a data ranging bucket thatincludes data corresponding to the discrete frequencies of 4, 8, 12, . .. 248, 252, and 256 (based on RS256) and the portion of digital datathat corresponds to the imaging data is placed in an imaging data bucketthat includes data corresponding to the discrete frequencies of 129,130, 131, . . . , 190, 191, and 192 (based on RS256). In this example,the discrete frequencies of 132, 136, 140, . . . , 184, 188, and 192will be placed in both the ranging data bucket and the imaging databucket such that only the data associated with every fourth discretefrequency from the scanned range of 129, 130, 131, . . . , 190, 191, and192 (Δf=15.625 MHz) will be placed in the data ranging bucket. In anembodiment, the demultiplexing or extracting of the data into the properbuckets for further processing is implemented in the digital basebandsystem or in a CPU and the ranging and imaging buckets may beimplemented as logical constructs in the digital baseband system and/orthe CPU. Thus, the digital control of step size and frequency range in astepped frequency radar system enables simultaneous capture of rangingdata and imaging data via a non-overlapping stepped frequency scanningoperation using a single sensor system. Although the demultiplexing orextracting of stepped frequency scanning data into specific buckets isdescribed with reference to simultaneous capture of ranging and imagingdata, the concept of demultiplexing or extracting of stepped frequencyscanning data into specific buckets for subsequent processing can beimplemented for other applications.

In an embodiment, the entire frequency range, e.g., the entire 2-6 GHzfrequency range, could be scanned with a step size of, for example,Δf=16.625 MHz (RS256), and ranging and imaging data could be extractedat different multiples of the step size from the set of digital datathat is generated from the scan. For example, for ranging, only datagenerated from every fourth frequency pulse is processed, e.g., a stepsize of Δf=62.5 MHz, and for imaging, data generated from everyfrequency pulse in the 4-5 GHz frequency range is processed, e.g., astep size of Δf=16.625 MHz in the 4-5 GHz frequency range. In anembodiment, the multiples used for extraction are integer multiples,e.g., 1, 2, 3, 4, etc. of the step size at which the frequency range wasscanned. FIG. 18C illustrates digital frequency coding (in a timesequence) for the stepped frequency scanning illustrated in FIG. 18A inwhich a single stepped frequency scan is performed across the 2-6 GHzfrequency range at a step size of Δf=16.625 MHz (RS256). At thetransmitter (TX), discrete frequencies are stepped at 16.625 MHz/stepacross the entire 2-6 GHz frequency range. Using the RS256 scale, thediscrete frequency pulses are identified as 1, 2, 3, 4, . . . 253, 254,255, 256. Reflections corresponding to the transmitted frequency pulsesare received in the same sequential order at the receiver (RX) of thesensor system 1810 and processed. With reference to the receiveoperation, FIG. 18C illustrates that the discrete frequency pulses ofthe transmitted stream are received in the same sequential order (intime) as they are transmitted. The receiver then places ranging data ina “ranging data bucket” 1820 and places imaging data in a different“imaging data bucket” 1822. In particular, as illustrated in FIG. 18A,the ranging scan involves discrete frequency pulses at a step size of62.5 MHz across the frequency range of 2-6 GHz and the imaging scaninvolves discrete frequency pulses at a step size of 15.625 MHz acrossthe frequency range of 4-5 GHz. Thus, with reference to the left side ofthe receive operation, the portion of digital data that corresponds tothe ranging data is placed in the data ranging bucket 1820 that includesdata corresponding to the discrete frequencies of 4, 8, 12, . . . 248,252, and 256 (based on RS256) (e.g., an extraction multiple of “4” overthe frequency range of interest) and the portion of digital data thatcorresponds to the imaging data is placed in the imaging data bucket1822 that includes data corresponding to the discrete frequencies of129, 130, 131, . . . , 190, 191, and 192 (based on RS256) (e.g., anextraction multiple of “1” over the frequency range of interest). Inthis example, the discrete frequencies of 132, 136, 140, . . . , 184,188, and 192 will be placed in both the ranging data bucket and theimaging data bucket and only the data associated with every fourthdiscrete frequency will be placed in the data ranging bucket. Thedemultiplexing or extracting of the data into the proper buckets forfurther processing is implemented in digital baseband system or in a CPUand the ranging and imaging buckets may be implemented as logicalconstructs in the digital baseband system and/or the CPU. Thus, thedigital control of step size and frequency range in a stepped frequencyradar system enables simultaneous capture of ranging data and imagingdata via a non-overlapping stepped frequency scanning operation using asingle sensor system.

In an embodiment, multiple sensor systems such as the sensor systemdescribed with reference to FIGS. 6-8 may be located near enough to eachother such that the transmitted stepped frequency pulses may interferewith one another. For example, the sensor systems may be located nearenough to each other in a house or building that transmitted frequencypulses and reflected RF energy may intermingle between the two sensorsystems. FIG. 19A depicts an area 1902 (such as a room, a house, or abuilding) that includes two sensor systems (including TX₁/RX₁ andTX₂/RX₂), such as the sensor systems described above with reference toFIGS. 6-8, which may interfere with each other during stepped frequencyscanning. Thus, if TX₁ and TX₂ transmit frequency pulses at the samediscrete frequency and at the same time, the receivers, RX₁ and RX₂, mayexperience interference, which may degrade the quality of the rangingand/or imaging of the stepped frequency radar systems. However, in anembodiment, digital control of the frequencies of the discrete frequencypulses is used to encode the frequencies of the frequency pulses, e.g.,in a preprogrammed or pseudorandom fashion, so that the frequency pulsesof the two sensor systems are less likely or unlikely to interfere witheach other. That is, the frequency pulses are not transmitted in-orderor in-step, e.g., in sequential order (i.e., one step size increment perfrequency pulse transmission), but rather are transmitted “out-of-order”or “out-of-step,” which can reduce the likelihood of two frequencypulses from two different sensor systems interfering with each other.

FIG. 19B illustrates encoding and corresponding decoding of discretefrequency pulses transmitted from TX₁ and TX₂ of the sensor systems 1910depicted in FIG. 19A. In the example of FIG. 19B, both TX₁ and TX₂ aresimultaneously scanning across the 2-6 GHz frequency range at a stepsize of 15.625 MHz/step (e.g., RS256). Thus, each transmitter willtransmit 256 discrete frequency pulses to complete a scan across theentire 2-6 GHz frequency range, with the discrete frequency pulses beingidentified by the numeric values of 1-256. As illustrated in FIG. 19B,TX₁ transmits the 256 discrete frequency pulses in a first pseudorandomorder (e.g., 64, 17, 211, 12, 78, 94, . . . 2, 101, 112, 243, 16, 29,84, 6, 251) and simultaneously with TX₁, TX₂ transmits the same 256discrete frequency pulses in a second pseudorandom order (e.g., 14, 219,18, 256, 212, 47, . . . 5, 58, 141, 172, 3, 249, 11, 6, 4). In a casewhere the two sensor systems 1910 are close enough to each other,interfering RF energy (either reflected RF energy or RF energy directlyfrom the other transmitter) may be received at the sensor systems. Forexample, with reference to RX₁, RF energy corresponding to the stream ofdiscrete frequencies transmitted from TX₁ and RF energy corresponding tothe stream of discrete frequencies transmitted from TX₂ may be receivedsimultaneously at RX₁. However, because the receivers are using steppedfrequency radar, RX₁ is simultaneously receiving on the same frequencyat which TX₁ is transmitting such that when TX₁ transmits at frequency64, RX₁ receives at frequency 64. RX₁ may also be simultaneously exposedto RF energy at frequency 14 (generated from TX₂), but the RF energy atfrequency 14 will not be received (e.g., will not interfere withreceiving RF energy at frequency 64) since frequency 14 does not matchthe current transmission frequency (f_(TX1)=64) of TX₁. The receiver,RX₁, is then able to generate scan data associated with each transmittedfrequency pulse and re-order the data in a sequential order (e.g., 1, 2,3, . . . , 254, 255, 256) that allows ranging and/or imaging data to begleaned from the received RF energy. As illustrated in FIG. 19B, RX₁ isable to re-order the data in an order that corresponds to thefrequencies of the range scale, e.g., 1, 2, 3, . . . 254, 255, 256.Likewise, when TX₂ transmits at frequency 14, RX₂ receives at frequency14. RX₂ may also be simultaneously exposed to RF energy at frequency 64(generated from TX₁), but the RF energy at frequency 64 will not bereceived (e.g., will not interfere with receiving RF energy at frequency14) since frequency 64 does not match the current transmission frequency(f_(TX2)=14) of TX₂. The receiver, RX₂, is then able to generate scandata associated with each transmitted frequency pulse and re-order thedata in a sequential order (e.g., 1, 2, 3, . . . , 254, 255, 256) thatallows ranging and/or imaging data to be gleaned from the received RFenergy. As illustrated in FIG. 19B, RX₂ is able to re-order the data inan order that corresponds to the frequencies of the range scale, e.g.,1, 2, 3, . . . 254, 255, 256. Using the above-described technique,encoding of the discrete frequency pulses (e.g., preprogrammed orpseudorandom encoding) can be used to avoid interference between twosensor systems that are located within range of each other. In theexample of FIG. 19B, given a pseudorandom pattern of 256 discretefrequencies, the likelihood of the two sensor systems transmittingfrequency pulses at the same frequency at the same time can be estimatedas 1/256×1/256=1.5×10⁻⁷ chance of interference. Although the example isdescribed with only two sensor systems, the encoding scheme can beapplied to more than two sensor systems and still provide a high degreeof protection against interference amongst sensor systems. In anembodiment, pseudorandom encoding may implemented by pseudorandom numbergenerators located within the sensor systems.

In an embodiment, ranging refers to detecting the linear distancebetween an object of interest and the sensor system using steppedfrequency scanning and imaging refers to detecting the spatial spread ofan object of interest relative to the sensor system. In a threedimensional coordinate system of x, y, and z, the ranging or range of anobject relative to a sensor system may be represented by digitalinformation that corresponds to a linear distance relative to the z axisand the imaging or image of an object relative to the sensor system maybe represented by digital information that corresponds to the x and ydimensions of the object. In an embodiment, 2D imaging may refer toinformation corresponding to the x and y dimensions of an object withoutranging information and 3D imaging may refer to information thatcombines ranging information with 2D imaging information to producethree-dimensional information about an object relative to the sensorsystem.

In an embodiment, an RF front-end is configured to support a wider rangeof frequencies. FIG. 20 depicts and embodiment of an RF front-end thatis configured to support a 2-6 GHz frequency range and a 122-126 GHzfrequency range. The RF front-end is similar to the FR front-enddescribed with reference to FIG. 7 and thus similar reference numbersare used to identify similar components. In the embodiment of FIG. 20,the elements include a crystal oscillator 770, a phase locked loop (PLL)772, a bandpass filter (BPF) 774, a mixer 776, power amplifiers (PAs)778, TX antennas 744, a frequency synthesizer 780, a frequency doubler782, a frequency divider 784, a mixer 786, an RX antenna 746, a lownoise amplifier (LNA) 788, a mixer 790, a mixer 792, and an IntermediateFrequency/Baseband (IF/BB) component 794. As illustrated in FIG. 20, thegroup of receive components identified within and dashed box 796 isrepeated four times, e.g., once for each of four distinct RX antennas.

Operation of the system shown in FIG. 20 is described with reference toa transmit operation and with reference to a receive operation. Thedescription of a transmit operation generally corresponds to aleft-to-right progression in FIG. 20 and description of a receiveoperation generally corresponds to a right-to-left progression in FIG.20. With regard to the transmit operation, the crystal oscillator 770generates an analog signal at a frequency of 10 MHz. The 10 MHz signalis provided to the PLL 772, to the frequency synthesizer 780, and to thefrequency divider 784. The PLL uses the 10 MHz signal to generate ananalog signal that is in the 2-6 GHz frequency range. The 2-6 GHz signalis provided to the BPF 774, which filters the input signal and passes asignal in the 2-6 GHz range to the mixer 776. The 2-6 GHz signal is alsoprovided to the mixer 786.

Dropping down in FIG. 20, the 10 MHz signal is used by the frequencysynthesizer 780 to produce a 15 GHz signal. The 15 GHz signal is used bythe frequency doubler 782 to generate a signal at 120 GHz. In anembodiment, the frequency doubler includes a series of three frequencydoublers that each double the frequency, e.g., from 15 GHz to 30 GHz,and then from 30 GHz to 60 GHz, and then from 60 GHz to 120 GHz. The 120GHz signal and the 2-6 GHz signal are provided to the mixer 776, whichmixes the two signals to generate a signal at 122-126 GHz depending onthe frequency of the 2-6 GHz signal. The 122-126 GHz signal output fromthe mixer 776 is provided to the power amplifiers 778, and RF signals inthe 122-126 GHz range are output from the TX antennas 744. In anembodiment, the 122-126 GHz signals are output at 15 dBm (decibels (dB)with reference to 1 milliwatt (mW)). In an embodiment, the PLL iscontrolled to generate discrete frequency pulses between 2-6 GHz thatare used for stepped frequency transmission.

The 10 MHz signal from the crystal oscillator 770 is also provided tothe frequency divider 784, which divides the frequency down, e.g., from10 MHz to 2.5 MHz via, for example, two divide by two operations, andprovides an output signal at 2.5 MHz to the mixer 786. The mixer 786also receives the 2-6 GHz signal from the BPF 774 and provides a signalat 2-6 GHz+2.5 MHz to the mixer 792 for receive signal processing.

With reference to a receive operation, electromagnetic (EM) energy isreceived at the RX antenna 746 and converted to electrical signals,e.g., voltage and current. For example, electromagnetic energy in the122-126 GHz frequency band is converted to an electrical signal thatcorresponds in frequency (e.g., GHz), magnitude (e.g., power in dBm),and phase to the electromagnetic energy that is received at the RXantenna. The electrical signal is provided to the LNA 788. In anembodiment, the LNA amplifies signals in the 122-126 GHz frequency rangeand outputs an amplified 122-126 GHz signal. The amplified 122-126 GHzsignal is provided to the mixer 790, which mixes the 120 GHz signal fromthe frequency doubler 782 with the received 122-126 GHz signal togenerate a 2-6 GHz signal that corresponds to the electromagnetic energythat was received at the RX antenna. The 2-6 GHz signal is then mixedwith the 2-6 GHz+2.5 MHz signal at mixer 792 to generate a 2.5 MHzsignal that corresponds to the electromagnetic energy that was receivedat the RX antenna. For example, when a 122 GHz signal is beingtransmitted from the TX antennas and received at the RX antenna, themixer 792 receives a 2 GHz signal that corresponds to theelectromagnetic energy that was received at the antenna and a 2 GHz+2.5MHz signal from the mixer 786. The mixer 792 mixes the 2 GHz signal thatcorresponds to the electromagnetic energy that was received at the RXantenna with the 2 GHz+2.5 MHz signal from the mixer 786 to generate a2.5 MHz signal that corresponds to the electromagnetic energy that wasreceived at the RX antenna. The 2.5 MHz signal that corresponds to theelectromagnetic energy that was received at the RX antenna is providedto the IF/BB component 794 for analog-to-digital conversion. Theabove-described receive process can be implemented in parallel on eachof the four receive paths 796. As is described here, the systemdescribed with reference to FIG. 20 can be used to generate variousdiscrete frequencies that can be used to implement, for example, steppedfrequency radar detection. As described herein, multiple mixingoperations are performed to implement a sensor system at such a highfrequency, e.g., in the 122-126 GHz range. The multiple mixers andcorresponding mixing operations implement a “compound mixing”architecture that enables use of such high frequencies.

In an embodiment, the sensor system, or components thereof, can becombined with other sensor systems to form a sensor system that includesa larger sensor array. For example, multiple sensor systems, such as thesensor systems as described above, can be arranged into a 2D array toform a multi-sensor sensor system. In one embodiment, four sensorsystems are configured in a rectangular 2D array, such that the combinedarray includes eight TX antennas and sixteen

RX antennas. FIG. 23A depicts an embodiment of a 2×2 array of sensorsystems 2110 (also referred to as RF units, or RFUs) such as the sensorssystems described above along with a frequency controller 2104 thatcombine to form a multi-sensor sensor system. In an embodiment, thefrequency controller can individually control the scanning frequenciesof each of the RF units. For example, the RF units can be controlled tosimultaneously transmit frequency pulses at different frequencies toimplement stepped frequency scanning in a manner that avoidsinterference amongst the RF units. The frequency controller can beimplemented in hardware, software, firmware, or a combination thereof.

As described above, the frequency controller 2104 can control the RFunits 2110 to simultaneously transmit frequency pulses at differentfrequencies to implement stepped frequency scanning in a manner thatavoids interference amongst the RF units. FIG. 21B illustrates anexample operating scenario (in a graph of frequency vs. time) in whichthe RF units simultaneously implement stepped frequency scanning acrossdifferent frequency sub-bands of the 2-6 GHz frequency band in a mannerthat avoids interference. As illustrated in FIG. 23B, RF unit 1transmits stepped frequency pulses in the frequency range of 2-3 GHz, RFunit 2 transmits stepped frequency pulses in the frequency range of 3-4GHz, RF unit 3 transmits stepped frequency pulses in the frequency rangeof 4-5 GHz, and RF unit 4 transmits stepped frequency pulses in thefrequency range of 5-6. In the operating scenario illustrated in FIG.21B, all of the RF units scan across their corresponding frequencyranges using a first step size, e.g., Δf=15.625 MHz/step (e.g., RS256)for a period of time that corresponds to two full sweeps of thecorresponding frequency ranges. The same step size amongst the four RFunits is represented in that the scan lines all have the same slope.Then, within the frequency ranges covered by RF units 2 and 3, there issomething of interest detected from the received signals. For example,the scanning may have detected a person and/or a person carrying onobject of interest such as a weapon. Thus, as illustrated in FIG. 21B,the RF units 2 and 3 change their step sizes to smaller step sizes andto narrow frequency ranges at targeted frequency bands, which smallerstep sizes and targeted frequency bands may be better for identifyingobjects such as weapons. As illustrated in FIG. 21B, the smaller stepsizes for RF units 2 and 3 are represented by the lower slope of thescan lines that correspond to the stepped frequency scanning during theperiod of time that corresponds to the next four sweeps and the smallerfrequency ranges and targeted frequency bands are represented by thevertical displacement (frequency range) and vertical location (targetedfrequency bands) of the scan lines. Additionally, the step sizesimplemented by the RF units may change as indicated by the change inslope between the third sweep and the fourth sweep. At some point, thesensor system may decide to return to a sweep configuration that isbetter suited for ranging as opposed to imaging. FIG. 21B illustratesthat in sweep seven, all of the RF units in the system return tosweeping across their original frequency bands at the original stepsize, e.g., Δf=15.625 MHz/step (e.g., RS256), which may be better suitedfor ranging as opposed to imaging. As illustrated in FIG. 21B, the fourRF units perform simultaneous stepped frequency scanning acrossnon-interfering frequency ranges in a manner that enables multiplefrequency bands to be simultaneously scanned without interfering witheach other. Thus, digital control of discrete frequencies in a steppedfrequency radar system provides spectral agility that can be utilized toimplement a multi-sensor system that can be used to implement rangingand 2D or 3D scanning in useful applications such as securitymonitoring.

In an embodiment, signal processing to implement ranging and 2D or 3Dimaging can be implemented in part or in full digitally by a DSP and/ora CPU. FIG. 22 is an embodiment of a DSP 2264 that includes a rangingcomponent 2274 and an imaging component 2276. Although the DSP is shownas including the two components, the DSP may include fewer componentsand the DSP may include other digital signal processing capability. TheDSP may include hardware, software, and/or firmware or a combinationthereof that is configured to implement the digital signal processingthat is described herein. In an embodiment, the DSP may be embodied asan ARM processor (Advanced RISC (reduced instruction set computing)Machine). In some embodiments, components of a DSP can be implemented inthe same IC device as the RF front-end and the TX and RX antennas. Inother embodiments, components of the DSP are implemented in a separateIC device or IC devices.

In an embodiment, the transmission of millimeter radio waves and theprocessing of signals that correspond to received radio waves is adynamic process that operates to locate signals corresponding to thedesired object (e.g., a person and/or a person carrying a weapon) and toimprove the quality of the desired signals (e.g., to improve the SNR).For example, the process is dynamic in the sense that the process is aniterative and ongoing process as the location of the sensor systemrelative to a vein or veins changes.

Beamforming is a signal processing technique used in sensor arrays fordirectional signal transmission and/or reception. Beamforming can beimplemented by combining elements in a phased antenna array in such away that signals at particular angles experience constructiveinterference while other signals experience destructive interference.Beamforming can be used in both transmit operations and receiveoperations in order to achieve spatial selectivity, e.g., to isolatesome received signals from other received signals.

In an embodiment, the techniques described herein are application tomonitoring a health parameter of a person, for example, monitoring theblood glucose level in a person, or to monitoring other parameters of aperson's health such as, for example, blood pressure and heart rate. Forexample, the reflectively of blood in a vessel such as the basilic veinwill change relative to a change in blood pressure. The change inreflectivity as monitored by the sensor system can be correlated to achange in blood pressure and ultimately to an absolute value of aperson's blood pressure. Additionally, monitored changes in bloodpressure can be correlated to heart beats and converted over time to aheart rate, e.g., in beats per minute. In other embodiments, thedisclosed techniques can be used to monitor other parameters of aperson's health that are affected by the chemistry of the blood. Forexample, the disclosed techniques may be able to detect changes in bloodchemistry that correspond to the presence of foreign chemicals such asalcohol, narcotics, cannabis, etc. The above-described techniques mayalso be able to monitor other parameters related to a person, such asbiometric parameters.

The above-described techniques may be used to monitor a health parameter(or parameters) related to blood in a blood vessel or in blood vesselsof a person. The blood vessels may include, for example, arteries,veins, and/or capillaries. The health monitoring technique can targetblood vessels such as the basilic and/or cephalic veins and/or vesselsother than the basilic and/or cephalic veins. For example, othernear-surface blood vessels (e.g., blood vessels in the subcutaneouslayer) such as arteries may be targeted. Additionally, locations aroundthe wrist or locations other than the wrist area can be targeted forhealth monitoring. For example, locations in around the ear may be adesirable location for health monitoring, including, for example, thesuperficial temporal vein and/or artery and/or the anterior auricularvein or artery. In an embodiment, the sensor system may be integratedinto a device such as a wearable device (e.g., a watch) or anotherdevice such as a smartphone or a standalone health monitoring device.

In an embodiment, health monitoring using the techniques describedabove, may involve a calibration process. For example, a calibrationprocess may be used for a particular person and a particular monitoringdevice to enable desired monitoring quality.

Although the techniques are described as using frequency ranges of 2-6GHz and 122-126 GHz, some or all of the above-described techniques maybe applicable to frequency ranges other than 2-6 GHz and 122-126 GHz.For example, the techniques may be applicable to frequency ranges around60 GHz. In an embodiment, a system similar to that described withreference to FIG. 6 may be used to implement health monitoring bytransmitting and receiving RF energy in the 2-6 GHz range and/or in the122-126 GHz. For example, health monitoring may be implemented usingboth the 2-6 GHz frequency range and the 122-126 GHz frequency range.For example, in an embodiment, stepped frequency scanning in implementedin the lower frequency range and then in the higher frequency range, orvice versa. Using multiple non-contiguous frequency ranges (e.g., boththe 2-6 GHz frequency range and the 122-126 GHz frequency range) mayprovide improved accuracy of health monitoring.

Although the operations of the method(s) herein are shown and describedin a particular order, the order of the operations of each method may bealtered so that certain operations may be performed in an inverse orderor so that certain operations may be performed, at least in part,concurrently with other operations. In another embodiment, instructionsor sub-operations of distinct operations may be implemented in anintermittent and/or alternating manner.

It should also be noted that at least some of the operations for themethods described herein may be implemented using software instructionsstored on a computer useable storage medium for execution by a computer.As an example, an embodiment of a computer program product includes acomputer useable storage medium to store a computer readable program.

The computer-useable or computer-readable storage medium can be anelectronic, magnetic, optical, electromagnetic, infrared, orsemiconductor system (or apparatus or device). Examples ofnon-transitory computer-useable and computer-readable storage mediainclude a semiconductor or solid state memory, magnetic tape, aremovable computer diskette, a random access memory (RAM), a read-onlymemory (ROM), a rigid magnetic disk, and an optical disk. Currentexamples of optical disks include a compact disk with read only memory(CD-ROM), a compact disk with read/write (CD-R/W), and a digital videodisk (DVD).

Alternatively, embodiments of the invention may be implemented entirelyin hardware or in an implementation containing both hardware andsoftware elements. In embodiments which use software, the software mayinclude but is not limited to firmware, resident software, microcode,etc.

Although specific embodiments of the invention have been described andillustrated, the invention is not to be limited to the specific forms orarrangements of parts so described and illustrated. The scope of theinvention is to be defined by the claims appended hereto and theirequivalents.

What is claimed is:
 1. A stepped frequency radar system, the systemcomprising: components for: performing stepped frequency scanning acrossa frequency range using frequency steps of a step size, the steppedfrequency scanning performed using at least one transmit antenna and atwo-dimensional array of receive antennas; changing at least one of thestep size and the frequency range; and performing stepped frequencyscanning using the at least one transmit antenna and the two-dimensionalarray of receive antennas and using the changed at least one of the stepsize and the frequency range.
 2. The stepped frequency radar system ofclaim 1, wherein the at least one of the step size and the frequencyrange is changed in accordance with a digital frequency control signal.3. The stepped frequency radar system of claim 1, wherein the step sizeis changed from a first step size to a second step size, wherein thesecond step size is smaller than the first step size.
 4. The steppedfrequency radar system of claim 1, wherein the frequency range ischanged from a first frequency range to a second frequency range,wherein the first frequency range and the second frequency range areseparated by a third frequency range.
 5. The stepped frequency radarsystem of claim 4, wherein the third frequency range is learned byscanning the first, second, and third frequency ranges with a poweramplifier corresponding to the transmit antenna deactivated.
 6. Thestepped frequency radar system of claim 1, wherein the step size ischanged from a first step size to a second step size in response tofeedback information from the stepped frequency scanning.
 7. The steppedfrequency radar system of claim 1, wherein the step size is changed froma first step size to a second step size according to preprogrammedfrequency control signals.
 8. The stepped frequency radar system ofclaim 1, wherein the frequency range is changed from a first frequencyrange to a second frequency range in response to feedback informationfrom the stepped frequency scanning.
 9. The stepped frequency radarsystem of claim 1, wherein the frequency range is changed from a firstfrequency range to a second frequency range according to preprogrammedfrequency control signals.
 10. The stepped frequency radar system ofclaim 1, further comprising: evaluating data generated from the steppedfrequency scanning across the frequency range; and wherein the at leastone of the step size and the frequency range is changed in response tothe data evaluation.
 11. The stepped frequency radar system of claim 1,wherein evaluating data generated from the stepped frequency scanningacross the frequency range comprises identifying an increase inmagnitude of received RF energy at wavelengths that correspond to knownresonant resonant wavelengths of a weapon.
 12. The stepped frequencyradar system of claim 1, wherein the frequency range is in the range of2-6 GHz.
 13. The stepped frequency radar system of claim 1, wherein thecomponents are further configured for: changing from the second stepsize to a third step size, wherein the third step size is different fromthe second step size; and performing stepped frequency scanning acrossthe third frequency range using frequency steps of a third step size.14. The stepped frequency radar system of claim 13, wherein the thirdstep size is smaller than the second step size.
 15. The steppedfrequency radar system of claim 1, wherein the step size is changed froma first step size to a second step size, wherein the second step size issmaller than the first step size and wherein the frequency range ischanged from a first frequency range to a second frequency range,wherein the first frequency range is wider than the second frequencyrange.
 16. A stepped frequency radar system, the system comprising: aradio frequency (RF) front-end including at least one transmit antennaand a two-dimensional array of receive antennas, the RF front-endconfigured to: perform stepped frequency scanning across a frequencyrange using frequency steps of a step size, the stepped frequencyscanning performed using the at least one transmit antenna and thetwo-dimensional array of receive antennas; change at least one of thestep size and the frequency range; and perform stepped frequencyscanning using the at least one transmit antenna and the two-dimensionalarray of receive antennas.
 17. The stepped frequency radar system ofclaim 16, wherein the at least one of the step size and the frequencyrange is changed in accordance with a digital frequency control signalreceived at the RF front-end.
 18. The stepped frequency radar system ofclaim 16, wherein the step size is changed from a first step size to asecond step size, wherein the second step size is smaller than the firststep size.
 19. The stepped frequency radar system of claim 16, whereinthe frequency range is changed from a first frequency range to a secondfrequency range, wherein the first frequency range and the secondfrequency range are separated by a third frequency range.
 20. Thestepped frequency radar system of claim 19, wherein the third frequencyrange is learned by scanning the first, second, and third frequencyranges with a power amplifier corresponding to the at least one transmitantenna deactivated.
 21. The stepped frequency radar system of claim 16,wherein the step size is changed from a first step size to a second stepsize in response to feedback information from the stepped frequencyscanning.
 22. The stepped frequency radar system of claim 16, whereinthe step size is changed from a first step size to a second step sizeaccording to preprogrammed frequency control signals.
 23. The steppedfrequency radar system of claim 16, wherein the frequency range ischanged from a first frequency range to a second frequency range inresponse to feedback information from the stepped frequency scanning.24. The stepped frequency radar system of claim 16, wherein thefrequency range is changed from a first frequency range to a secondfrequency range according to preprogrammed frequency control signals.25. The stepped frequency radar system of claim 16, further comprising:evaluating data generated from the stepped frequency scanning across thefrequency range; and wherein the at least one of the step size and thefrequency range is changed in response to the data evaluation.
 26. Thestepped frequency radar system of claim 59, wherein evaluating datagenerated from the stepped frequency scanning across the frequency rangecomprises identifying an increase in magnitude of received RF energy atwavelengths that correspond to known resonant resonant wavelengths of aweapon.
 27. The stepped frequency radar system of claim 16, wherein thefrequency range is in the range of 2-6 GHz.
 28. The stepped frequencyradar system of claim 16, further comprising: changing from the secondstep size to a third step size, wherein the third step size is differentfrom the second step size; and performing stepped frequency scanningacross the third frequency range using frequency steps of a third stepsize.
 29. The stepped frequency radar system of claim 28, wherein thethird step size is smaller than the second step size.
 30. The steppedfrequency radar system of claim 16, wherein the step size is changedfrom a first step size to a second step size, wherein the second stepsize is smaller than the first step size and wherein the frequency rangeis changed from a first frequency range to a second frequency range,wherein the first frequency range is wider than the second frequencyrange.